This shutter is the last component in 3-ID-A. When this shutter is closed, the beam can travel no further than this station, into the B, C, or D downstream stations. Most Users, when not taking data, will have this shutter closed, yet have their Front End Shutter (PS2) open. With PS2 open, the beam continuously strikes the monochromator crystals. This constant heat load allows them to achieve thermal equilibrium which is necessary for good data collection.